<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>bootstrap</title>
    <link rel="stylesheet" href="bootstrap/css/bootstrap.min.css">
    <script src="jquery/jquery-3.3.1.js"></script>
    <script src="bootstrap/js/bootstrap.min.js"></script>
</head>
<body>
    <div class="dropdown">
        <button class="btn btn-default dropdown-toggle" data-toggle="dropdown">
            这是按钮
            <span class="caret"></span>
        </button>
        <ul class="dropdown-menu">
            <li>
                <a href="#">慕课网</a>
            </li>
            <li>
                <a href="#">慕课网</a>
            </li>
            <li>
                <a href="#">慕课网</a>
            </li>
        </ul>
    </div>
</body>
</html>